| Temporal order memory means memory of the event sequence one has already experienced, which is different from item or event memory. It is always evaluated by the paradigm of recency judgment:Present a serial of stimulant targets first, then show two probes which are selected from the previous targets randomly and one should choose the probe which was presented earlier or later. The temporal distance effect has been reported, that is, the closer the temporal distance between the two probes, the shorter reaction time and the higher correct rate. On the contrary, the longer for reaction time and the lower for correct rate.With recency judgment paradigm, Milner et al. have researched temporal order emory in the patients suffering from brain injury. Taking verbal and non-verbal picture as memory material, their results showed that the patients of frontal lobe damage performed worse in temporal order memory while the patients of the temporal lobe damage performed worse in recognition memory. At the same time the patients with both the temporal lobe and frontal lobe damage performed badly in both recognition memory task and temporal order memory task. Follow-up researches further confirm these results. In addition, the Korsakov syndrome, Alzheimer's patients and other studies also showed that temporal order memory damaged. Fabiani et al. found that the elderly performed worse in temporal order memory compared with young men. But there is no significant difference between the elderly with young people. So, they proposed that the elderly faired in temporal order memory task because of their frontal lobe's dysfunction. More evidences the idea that the inability to perform strategic operations leads to deficits in temporal order memory. Hence it may be that patients with damage to frontal lobe have difficulty with temporal order memory tasks not because the frontal lobe codes order, but rather because areas outside of the frontal lobe that encode order are not called to action by the frontal lobe. For example, patients with frontal lobe damage did not inhibit irrelevant information, So these patients are more susceptible to interference than other patients, and such tasks require temporal order information. The exact role of frontal cortex in the temporal memory remained to be clarified.Temporal distance effect was also founded in the experiment which mice were subjects. In which confirmed that the medial prefrontal cortex involved in spatial memory processes information related to temporal order. In the eight-arm maze task experiments, the results showed that, compared with the control group mice, the medial prefrontal cortex damage mice performed badly in temporal order memory tasks, supporting participation that the medial prefrontal cortex associated with spatial temporal order information processes. Ninokura based on monkeys considered that the dorsolateral prefrontal cortex play an important monitoring and treatment role on temporal order information at the cellular level. However, Hoge et al. have shown that the ventral hippocampal CA1 sub-region play an important part on visual temporal order information without affecting the visual object detection in mice. Howland showed that temporal order memory was supported by marginal areas, including the ventral hippocampus and medial prefrontal cortex. In short, the network of temporal order memory of brain regions involved in memory there is no consistent conclusion.Functional magnetic resonance imaging provided neural mechanism in temporal order memory. Ce'line observed that the central dorsal lateral prefrontal cortex-burro Friedman partition (Brodmann area, BA) 9/46 involved in memory encoding of visual temporal order information. However, Konishi supported that these areas invovlving in temporal order memory, including the lateral prefrontal cortex on both sides of centro-frontal (BA9), the left side of the lower part of the lateral prefrontal cortex (BA45/44), the left side of anterior prefrontal cortex (BA10/46), both sides of the medial temporal lobe (BA28/35). In summary, The low temporal resolution of functional neuroimaging cause the difficulty of distinguishing the order of involvement of brain regions.In this paper, we used the advantages of high temporal resolution of event-related potentials (event-related potentials, ERP) to explore the working memory of temporal information extraction and activation of related brain areas, and investigate neural mechanism of temporal distance effect.Eighteen college students (8 males and 10 females) aged between 24 and 28 years were recruited. All participants reported corrected to normal visual acuity. right-handed. The experiment was conducted in accordance with the Declaration of Helsinki and all subjects received Y40.00 for their participation. The experiment takes 40 minutes averagely for each participant.The subjects were presented a circular of different colors in the center of the black screen. The distance between subjects and screen is 100 cm. The colors were selected from yellow, red, green and blue etc. In temporal order memory task, the subjects were instructed to determine which color appeared more recently. In recognition memory task, the subjects were instructed to choose which color appeared, while in control task the subjects were instructed to judge which side of the gray circle appears in the screen.There were three blocks:temporal order memory task, recognition memory task, control task. The order of three groups and left and right buttons were counterbalanced between subjects.Each pattern presented 400 ms, followed by black blank screen for 400 ms. Reactions were valid between 100 ms and 1000 ms. The response keys were counterbalanced between subjects. There were 20 sec for participants to have a rest every 2 min interval within blocks and 3 min break between blocks.EEG (bandpass 0.5-100 Hz) was recorded using an ERP system developed in our lab, which could record behavior and EEG data. It was sampled from 19 electrodes mounted in a elastic cap according to international 10-20 system referenced to both earlobes. Frontal midline site (Fz) was grouding ERP epochs were extracted off-line and included 100 ms of pre-stimulus activity and of 1000 ms post-stimulus activity for three tasks. Baseline was from-100 ms to 0 ms. Artifact above 70μV was eliminated manually. Data from one participants were excluded because excessive blink or over lowering correct rate.One way ANOVA and paired t test were performed for three tasks and two tasks respectively. The response time and correct rates were analyzed using SPSS 13.0 based on Greenhouse-Geissor correction. ERP data was analyzed using self-developed statistical software. We performed one way ANOVA for three tasks trials based on lower-bound epsilon. Statistical parametric mapping F-values [SPM(F)] and t-values [SPM(t)] were gained from interpolation calculated by each channel's F-values or t-values respectively. The significant level was 0.05. SPM(t) was corrected with Bonferroni correction. The temporal distance effect is significant:the closer targets correspond to longer reaction time [745.47±106.15,711.67±102.17,653.73±81.45 (ms):F(1.28 20.48)=43.336, P=0.000] and higher error rate [62.76±7.05,72.47±5.35,84.47±6.37 (%); F(1.32,21.11)=132.602, P=0.000]. Significant behavioral effect of the task factor was also found for both reaction time [F(1.32,21.11)=135.989, P=0.000] and error rate [F(2,32)=200.313, P= 0.000]. No significant behavioral difference was found between the temporal order group and the recognition group.In the maintenance phase,17 participants showed that:ERP waveforms from electrodes FP1, FP2, F3, F4, and Cz showed significant difference in three tasks. The difference between temporal order task and recognition task existed in left cerebral hemisphere (electrodes F7, F3, T3, and C3) and right hemisphere regions (electrodes F4, F8, C4). Differences between the three intervals is mainly reflected in the F3, F4, Cz and other areas, especial after P700. The ERP waveforms before P700 almost overlap in three intervals. In the retrieval phase 17 participants showed that:ERP waveforms from 300-500 ms (electrodes Fz, F4, Cz, C4) showed significant difference in three tasks, but there is no significant difference between temporal order memory task and recognition memory task. ERP waveforms from 500 ms (electrodes F3,T3,C3,P3) showed significant difference in temporal interval tasks.In the maintenance phase, SPM showed the task effect was SPM showed that the task effect was seen bilateral temporal parietal (280-360 ms), the top bilateral occipital (380-440 ms), almost the entire brain (480-720 ms), in addition to other brain areas outside the occipital lobe (760-880 ms), and other brain regions outside the right frontal, temporal, parietal central (900-920 ms); Temporal interval significant difference was seen in the left temporal parietal lobe (420-430 ms), bilateral temporal-parietal occipital (440-460 ms), bilateral frontotemporal parietal (470-490 ms); Temporal order and recognition memory tasks were significantly fewer regional differences, Only in the left parietal lobe (460-500 ms,680-800 ms).In the retrieval phase, SPM showed that the task effect was seen in the bilateral occipital lobe (200-220 ms); the right frontoparietal occipital lobe (240-260 ms), the left frontal, left temporal-parietal Leaf (360-400 ms), or occipital lobe prefrontal brain regions outside the most of the (440-640 ms), bilateral frontal, temporal lobe (680-760 ms), the left temporal lobe, right frontal lobe (800-820 ms). Temporal interval significant difference was seen in the left temporal lobe (260 ms-270 ms), bilateral occipital lobe the top (280-290 ms), except the majority of the prefrontal brain areas outside the (300-360 ms).In addition to frontal and prefrontal brain regions outside the most of the (380-390 ms), the top right occipital lobe (400-410 ms).Our results suggest that during the maintenance stage in work memory, temporal distance effect mainly existed in bilateral parietal lobes after the target stimulus appeared 440-480 ms. During the retrieval stage in memory, temporal distance effect mainly existed in bilateral parietal lobe after the probe stimulus appeared 300-400 ms. Moyer et al. reported number distance effect, that is, compared figures involved in the number of the farther apart, to determine more easily expressed as reaction time more shorter, the correct rate more higher. Marshuetz using uppercase letters as material, the same distance from the observed behavior of the performance effects, such as the comparison D/H with D/F letter from the former is reaction time more shorter and correct rate more higher; its report on top of functional magnetic resonance imaging Yet there was a significant distance effect, But not observed, the corresponding effect of the frontal lobe, Perhaps they think frontal lobe plays a more general monitoring role in the temporal order information processing. Those researches took numbers, letters as stimulus materials and their paradigms were based on long-term memory paradigm. Our results were similar to the above-mentioned previous researches with a working memory paradigm and suggest that the two types of memory paradigm, the time from the same number of letters from the same, may share a similar mechanism of neural processing.In this study, The differences in memory maintenance stage of between temporal order memory and recognition memory existed in the left parietal lobe after target stimulus appeared 480 ms,700-800 ms. There is no significant differences in memory retrieval stage of between temporal order memory and recognition memory in the behavioral and ERP, task effect in ERP mainly in two kinds of memory tasks and the control group tasks. Based on behavioral research, Fabiani considered that the frontal lobe may not be involved in memory encoding, curing and retrieval of aspects involved in the organization of memory, but only play a regulation role on the temporal order memory. Hauser and other studies also considered that the temporal order memory declined that may be age-related in the brain in mice. Ciaramelli, et al. further proposed "attention to memory" (attention to memory, AtoM) Hypothesis:In the episodic memory retrieval, superior parietal lobule supported a strategic retrieval process through the allocation of top-down attention resources, indirectly involved in the retrieval. the target memory is not automated elicited by external source but is a strategical search process mediated by prefrontal lobe which is needed attention resources. Inferior parietal lobule automatically attentional captured memory content retrieval mediated by the medial temporal lobe, which was a relatively automatic direct process involving retrieval process, mediated by the medial temporal lobe, required little attentional resources. Our results showed that the left parietal lobe not frontal or prefrontal lobe directly involved in maintenance stage of temporal order information, while there is no differences between temporal order memory and recognition memory during retrieval stage. So our results tend to support "attention to memory" Hypothesis, suggesting that parietal lobe involve encoding and retrieval stage of temporal order memory, But frontal lobe just indirectly used temporal information not involved storage. Therefore, the previous study found that frontal lobe damage affect the temporal order memory are more likely to occur in the monitoring phase. |
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